Category: general

Map-making is an inherently iterative process. Often finding an appropriate base layer is vital to providing a solid foundation for this process. In this spirit, I’ve been working on the digitization of the basic Public Land Survey System (PLSS), or the Cadastral Map series for both Portland and Seattle from the 1850s as base maps for the hidden hydrology studies of both cities. This data, which is the most uniform and complete snapshot of the landscape of the west, is a great resource for the locations of historic streams and other features. Because the use of the shared cartography of Townships with their corresponding Section grids, the PLSS maps provides a link to very accurately georeference the historic with the modern. Prior to diving into some of this work, I thought it prudent to discuss the Public Lands maps themselves.

There’s plenty of history out there for those in the mood, and my plan isn’t a deep dive, but more of some context. A good starting place is ‘The National Map’ page by the USGS on the subject of the PLSS, and a brief history page from the BLM. Everything else you may want to know about the Cadastral Survey is found at the Bureau of Land Management page of Tools, including the massive 1983 History of the Rectangular Survey System by C.A. White (46mb PDF). The terminology of the PLSS, is somewhat synonymous with the concept of Cadastral Survey, although in reality there is a difference, as one (PLSS) is the thing itself mapping the United States, and the other (Cadastral) a type of survey, defined as “having to do with the boundaries of land parcels.” Cadastral surveys of all types are done all over the world, and the origin comes from the “…Latin base term Cadastre referring to a registry of lands. So actually Cadastral Surveying is surveying having to do with determining and defining land ownership and boundaries” (via Cadastral Survey).

After the Revolutionary War, there was huge amounts of available land, and the need to distribute and sell tracts became necessary for the new survey. While the original colonies were laid out pre-PLSS using more traditional metes and bounds, but due to the immensity of the effort, Thomas Jefferson proposed a system of surveying massive open tracts of land. The Land Ordinance of 1785 set up the system and the subsequent 1787 Northwest Ordinance kick-started the process (although it referred to the areas NW of the colonies, not the actual NW Territories).

The surveying moved across the country over the next hundred years – as The extent of the surveying is captured in the map below, starting in Ohio and Florida on the east and encompassing the majority of the midwest, plains, and west including Alaska (which is still being surveyed today), with the only exception being Texas. Almost 1.5 billion acres were included.

Anyone who has looked at a survey will be familiar with the language of the PLSS. Any legal land description could be generated starting with“…the State, Principal Meridian name, Township and Range designations with directions, and the section number”. There are many versions of this diagram out there, but it breaks down the foundations of the PLSS using the Principal Meridians and Base Lines, and breaking the grid into Townships and the 36 smaller Sections.

The markers are vital to maintaining the integrity of the grid over centuries, and there are approximately 2.6 million section corners across the US. An interesting link to the ‘Corner Identification and Markings’ shows some of the layout specifics and one of the common protection measures employed for the corner monuments, circling the monument in a circle of stone. There is a shared geography continuity between the principal Willamette Meridian, established in 1851, with bisects both Portland and Seattle, and the shared baseline which runs parallel a bit south of the border between the two states.

“The Willamette Meridian was established June 4th, 1851 and runs from the Canadian border to the northern border of California. The base line runs from the Pacific Ocean to the Idaho border. All property in Washington and Oregon is referenced to this point. The original stake was replaced by a large stone in 1855 and is now part of The Willamette Stone Park in Portland.”

The PLSS is still updated, so if you want a deep dive in this topic, you can reference, the 1973 Manual of Surveying Instructions , which provides the most current info on PLSS surveying. Rather than a mere history lesson, the concept of the PLSS is vital to the understanding the ability to reference historical maps and . This is less important for East Coast but for a large portion of the United States, is the vital tool for hidden hydrology work. Also the extent of coverage that was all completed within a short timeframe (at least in local areas) provides a measure of comparability between areas.

A typical survey map shows the detail of the maps, in this case Township No. 1 N. Range No. 1 East, in the Willamette Meridian, with downtown Portland in the bottom of the map, and showing some of the topographic features, ponds, and streams. IN this case, the original 1852 map was redrawn in the early 1900s, which is pretty common. This info is downloadable via the BLM site.

And the typical surveyor notes, which are a tough read, but shows the information which was later interpreted by the mapmakers, based on the surveyors notations as they followed the specific section lines within the individual townships. The interpretation is a key item that implies the ‘filling in the blanks’ of these maps, as each line was not individually surveyed.

To see this in action, and to explain the correlation between georeferenced history maps and the modern GIS, you see the rectangular areas of the map Sections (this map is a composite of the map above (T01sn01e) and the Township below (T01s01e). This is the area in the Taggart neighborhood, in this case the upper Taggart Basin, showing the Willamette River (light blue), some small water bodies and streams (darker blue), as well as riparian wetlands (green).

The same area is georeferenced with modern GIS info (in this case the 2010 roads, parks, schools), and you can see the Section Lines (orange) that register on maps. The Taggart streams have long been buried, along with the filling of the wetlands along the Willamette for industrial lands. The modern topography is also shown, and you can see the tracings of the landscape channels still evident today.

The ability to tap into other map tools, in this case digital elevation ‘hillshade’ model (of the Lower Taggart Basin) again give some context for new and old, and graphically show some of the landform that exists today. There’s no shortage of analysis once the PLSS info is referenced. Lots more specific info on these maps in Portland and Seattle coming soon.

While amazingly detailed, the maps are, as mentioned, somewhat variable in nature due to the interpretation of survey notes and mapmaking. Thus, the PLSS becomes a great starting point, with good coverage and georeferencing, some they become a framework for overlaying other maps and data. Also, while the surveying standards were the same, as I will point out in a future posts, the quality and legibility of the maps often depended on the mapmakers themselves, and maps of one location could have very different information. This is evident from looking at Seattle versus Portland, and what i feel is a specific quality of maps in the latter versus the former.

Endnote: Having grown up in North Dakota, I was very aware both of the grid, and the ubiquitous grid-shift – as the rhythm of gravel roads cut through the state if perhaps more evident and legible when each ‘back road’ follows a grid. The excerpt below from Fathom shows the amount of contiguous one miles squares.

This making it infinitely possible to chart one’s path multiple ways to get to locations, and also comes with long stretches of arrow-straight road ending with a curve or more often a tee. Many a speeding or slightly inebriated driver was been surprised by this phenomenon. This comes up perusing such Instagram accounts like The Jefferson Grid, and for me more recently someone linked to re-posted from an article in Hyperallergic, featuring work of artist Gerco de Ruijter from 2015, as he masterfully documents this using a series of Google Earth images.

“By superimposing a rectangular grid on the earth surface, a grid built from exact square miles, the spherical deviations have to be fixed. After all, the grid has only two dimensions. The north-south boundaries in the grid are on the lines of longitude, which converge to the north. The roads that follow these boundaries must dogleg every twenty-four miles to counter the diminishing distances: Grid Corrections”